Implantable permanent and temporary medical electrical stimulation and/or sensing leads are well known in the fields of cardiac stimulation and monitoring, including cardiac pacing and cardioversion/defibrillation, and in other fields of electrical stimulation or monitoring of electrical signals or other physiologic parameters. In the field of cardiac stimulation and monitoring, the electrodes of epicardial or endocardial cardiac leads are affixed to the myocardium of the heart wall through either the epicardium or the endocardium, respectively, or bear against the epicardium or endocardium, respectively, or are lodged in a coronary vessel.
The lead body of a permanent or temporary cardiac lead typically includes one or more insulated conductive wires surrounded by an insulating outer sheath. Each conductive wire couples a proximal lead connector element with a distal stimulation and/or sensing electrode. Temporary and permanent cardiac leads having a single stimulation and/or sensing electrode at the lead distal end, a single conductor, and a single connector element are referred to as unipolar cardiac leads. Temporary and permanent cardiac leads having two or more stimulation and/or sensing electrodes at the lead distal end, two or more respective conductors, and two or more respective connector elements are referred to as bipolar lead or multi-polar leads, respectively.
Epicardial or myocardial permanent and temporary cardiac leads, or simply epicardial leads, are implanted by exposure of the epicardium of the heart typically through a limited thorocotomy or a more extensive surgical exposure made to perform other corrective procedures. Endocardial permanent and temporary cardiac leads, or simply endocardial leads, are implanted through a transvenous route to locate one or more sensing and/or stimulation electrode along or at the distal end of the lead in a desired implantation site in a chamber of the heart or a blood vessel of the heart. It is necessary to accurately position the electrode surface against the endocardium or within the myocardium or coronary vessel at the implantation site.
Temporary epicardial or endocardial cardiac leads are designed to extend through the patient's skin to an external monitor or pacing pulse generator to provide temporary pacing and to be removed from the patient's body when temporary pacing is halted. Permanent epicardial and endocardial cardiac leads are designed to be coupled to a pacemaker or defibrillator implantable pulse generator (IPG) or an implanted monitor and to be chronically implanted in the patient's body. The proximal end of such permanent cardiac leads typically is formed with one or more lead connector element that connects to a terminal of the IPG or monitor.
The complexity of the leads, the number of leads implanted in a common path, and the advancement of coronary sinus leads deep in a coronary vein have led to efforts to at least not increase and optimally to decrease the overall diameter of the cardiac lead body without sacrificing reliability and usability. More recently, it has been proposed to diminish the lead body further by eliminating the lumen for receiving the stiffening stylet and by reducing the gauge and coil diameter of the coiled wire conductor or replacing it with highly conductive stranded filament wires or cables. In bipolar or multi-polar leads, each such cable extends through a separate lumen of the lead body to maintain electrical isolation.
Over the last 30 years, it has become possible to reduce endocardial lead body diameters from 10 to 12 French (3.3 to 4.0 mm) down to 2 French (0.66 mm) presently through a variety of improvements in conductor and insulator materials and manufacturing techniques. The lead bodies of such small diameter, 2 French, endocardial leads must possess little if any column strength that could cause the lead distal end fixation mechanism and electrode to perforate through the myocardium during implantation and if the lead body were to become axially force-loaded during chronic implantation. As a result, the small diameter lead bodies lack “pushability”, that is the ability to advance the lead distal end axially when the lead proximal end is pushed axially, particularly when the lead body extends through the tortuous transvenous pathway.
Such small diameter endocardial leads typically then require distal fixation to maintain the electrode(s) at the desired implantation site. Active fixation helices that extend axially in alignment with the lead body to a sharpened distal tip and that have a helix diameter substantially equal to the lead body diameter are preferred because the fixation mechanism does not necessarily increase the overall diameter of the endocardial lead and is relatively robust, once the helix is screwed into the myocardium. Typically, but not necessarily, the fixation helix is electrically connected to a lead conductor and functions as a pace/sense electrode. In some cases, the lead body encloses one or more helical coiled or stranded wire conductor and lacks a lumen.
The lead bodies of such small diameter endocardial screw-in leads are so supple and flexible that it is difficult to rotate the lead distal end by application of rotary torque to the lead proximal end unless the lead body remains relatively straight and not confined by contact with vessel walls. This diminished “torqueability” prevents the rotation of the fixation helix at the lead distal end or renders the rotation unreliable once the lead body is advanced through a tortuous pathway and confined by contact against the vessel walls. To the degree that rotation torque can be transmitted from the lead proximal end to the lead distal end, the active fixation helix at the lead distal end can be over-rotated and screwed through the myocardium or under-rotated and not screwed into the myocardium sufficiently. Thus, it has been found necessary to use implantation instruments or tools that compensate for the lack of pushability and torqueability of the lead body.
A first technique of implantation of such miniaturized, highly flexible, endocardial screw-in leads involve the use of a guidewire that is first advanced through the tortuous transvenous pathway. The endocardial lead is then advanced through the pathway alongside or over the guidewire as disclosed in U.S. Pat. Nos. 5,003,990, 5,304,218, 5,902,331, 6,132,456, and 6,185,464, for example. Some of these techniques require that the lead body be configured to provide an over-the-wire connection and possess sufficient column strength to be advanced over the guidewire. Other techniques employ elongated pusher tools that have sufficient column strength applied against the lead body distal end and extending alongside the lead body and the over the guidewire. These techniques are relatively complex to execute. Moreover, the rotation of the active fixation helix at the lead distal end through rotation of the assembly can still be problematic.
In commonly assigned U.S. Pat. No. 5,246,014, the introducer distal end and the lead distal end are configured to interlock or engage one another. The catheter, introducer and sheath lead body are advanced together through the transvenous, tortuous pathway to locate the fixation helix near the implantation site in the right atrium, right ventricle, coronary sinus, or cardiac vein. The fixation helix is pushed out of the catheter lumen distal end and the introducer catheter is rotated to screw the fixation helix into the myocardium by pushing and rotating the introducer proximal end extending proximally out of the catheter lumen outside the patient's body. In this approach, the inner introducer extends, in use, all the way to the catheter distal end. Thus, the catheter distal segment is stiffened and may be difficult to advance through the tortuous pathway. Certain embodiments of the interlocking mechanism also increase the diameter of the lead distal end.
A further technique of implantation of such miniaturized endocardial screw-in leads disclosed in commonly assigned U.S. Pat. No. 5,897,584 employs a flexible guide catheter having a catheter body that has sufficient pushability and resistance to kinking that it can be advanced through the transvenous pathway. The lead body is inserted into a catheter lumen during advancement of the catheter distal end and fixation helix to the implantation site. Then, it is necessary to rotate the fixation helix from the proximal end of the assembly to screw it into the myocardium at the implantation site. The distal advancement and rotation of the fixation helix is facilitated by a torque transfer device that is temporarily fitted over a proximal segment of the lead body extending proximally outside of the guide catheter hub and at a distance therefrom corresponding to or a fraction of the distance that the fixation helix is to be advanced distally to rotate it into the myocardium.
The torque transfer device frictionally engages the lead body segment and can be manipulated with one hand to distally advance the fixation helix from the guide catheter lumen and screw it into the myocardium at the implantation site. The torque transfer device is slipped sideways over and removed from the proximal lead body segment through an elongated slot and installation/removal and retention characteristics depend on the relative width of the slot and diameter of the lead body.
This technique requires selection of catheter body materials and characteristics that ensures that the catheter lumen is constant in diameter and resists making abrupt changes in direction as the catheter is advanced through the twists and turns of the tortuous pathway. The lead body diameter and materials must be selected to minimize binding of the lead body against the catheter sidewall in the twists and turns. Generally speaking, it becomes easier to advance the lead body through the catheter lumen as the catheter lumen diameter is increased. But, increasing the catheter body lumen renders advancing the guide catheter through the twists and turns and into small diameter coronary vessels more difficult.
As noted in the above-referenced '584 patent, the guide catheter typically is supplied with a hemostasis valve attached to the catheter hub and a side port that permits introduction of saline and anticoagulants to flush and lubricate the catheter lumen. But, tightening of the hemostasis valve to eliminate leakage alongside the lead body can negatively influence the pushability and torqueability of the lead body by manipulation of the torque transfer device.
In another approach, the lead body is enclosed within the lumen of a further sheath or introducer, and the lead and introducer are disposed within the lumen of the guide catheter. The fixation helix is located within the catheter lumen during advancement of the lead distal end fixation helix through the transvenous pathway and heart chamber or coronary vessel to dispose the fixation helix near the implantation site.
In further commonly assigned U.S. Pat. No. 6,408,214, the inner introducer, referred to as an inner sheath, and the outer catheter, referred to as an outer sheath each have preformed curves formed in distal sheath segments so that multiple curves can be induced as the inner and outer sheaths are axially adjusted relative to one another. The materials and dimensions of the inner and outer sheaths are selected to provide pushability and torqueablity of the assembly with the small diameter lead body disposed in the inner sheath lumen. The inner sheath is longer than the outer sheath, so that it can be selectively moved out of the outer sheath lumen to advance its distal tip to the implantation site. Again, the fixation helix is pushed out of the catheter lumen distal end and then rotated to screw the fixation helix into the myocardium by pushing and rotating the introducer proximal end extending proximally out of the catheter lumen outside the patient's body.
These approaches disclosed in the above-referenced '214 and '584 patent can suffer from the frictional engagement and binding of the lead body against the inner sheath or introducer sidewall as the physician rotates the proximal lead body segment. If the inner sheath lumen is made relatively larger in diameter than the lead body diameter to avoid such binding, the lead body tends to wind up within the inner sheath lumen when it is rotated. Tactile feedback to the physician through the lead body of the rotation of the distal fixation helix as the proximal segment is rotated is lost due to binding or winding up within the sheath lumen. It is difficult for the physician to determine just how far the lead body distal segment has been advanced and how many rotations that the fixation helix has actually made.
Typically, it is only necessary to rotate the fixation helix the number of turns of the helix, e.g., two complete turns, to fully embed the helix into the myocardium. But, it may be necessary to rotate the proximal segment of the lead body through multiple turns, such as approximately four to nine turns, for example, depending on the lead length and the tortuosity of the pathway, to cause the applied torque to overcome windup of the lead body and rotate the distal fixation helix the requisite two turns. The physician cannot be certain that the distal fixation helix has rotated the requisite two turns or has over-rotated, possibly causing higher thresholds, and has perforated or is in danger of perforating through the myocardium.
Moreover, instruments, e.g., cardiac leads, guidewires, balloon catheters, etc advanced through guide catheter lumens typically are passed through a penetrable and re-sealable hemostasis valve incorporated into the guide catheter hub. The hemostasis valve bears against the instrument body to prevent leakage of fluids within the guide catheter lumen. Advancement of guidewires and balloon catheters and other instruments having column strength is not impeded by the contact with the hemostasis valve. However, it is difficult to pass cardiac leads of the types described above lacking appreciable column pushability and torqueability through such hemostasis valves.
Thus, a need remains for an introducer system for a small diameter screw-in lead lacking pushability and torqueability that enables advancement of the fixation helix through tortuous pathways into a wide variety of implantation sites in a heart chamber or in a coronary vessel of the left heart chambers and reliable fixation at the selected implantation site. Such a system is needed that provides the physician with positive feedback of the number of turns that the lead body is rotated to rotate the fixation helix the requisite number of turns into the myocardium. The above-described problem with the passage of a cardiac lead through a guide catheter hemostasis valve needs to be eliminated.
Preferably, such a lead introducer system would also be of use in implanting small diameter epicardial screw-in leads through minimally invasive approaches through the thorax to the epicardium of the heart, particularly implantation sites of the left heart chambers.